Git(Hub) and CVS

I know many here are using CVS, and many are also using git, so I wonder
if anybody can help me. On BSD.lv, I push my CVS repositories (kcgi,
sblg, etc.) to GitHub from time to time using a cvs2git script. It goes
as follows, shortened and pseudonymised:

REPO=$1 # e.g., kcgi
cd /tmp/cvs2git
cvs2git --blobfile=git-blob.dat \
--dumpfile=git-dump.dat \
--username=kristaps@me \
/path/to/cvsroot/$REPO
mkdir $REPO.git
cd $REPO.git
git init
cd .git
git fast-import \
--export-marks=../../git-marks.dat < ../../git-blob.dat
git fast-import \
--import-marks=../../git-marks.dat < ../../git-dump.dat
git remote add origin https://github.com/account/$REPO.git
cd ..
git checkout
git push --tags -u origin master

Our repositories are all pretty basic (just tags, no branches), and it's
only me pushing to GitHub, so this works although it's not incremental
and can take a minute or so. Or I should say it "worked", because since
updating OpenBSD from an embarrassingly old version, it doesn't any
more. The error given is on the push:

Compressing objects: 100% (633/633), done.
Writing objects: 100% (2257/2257), 492.44 KiB | 16.98 MiB/s, done.
Total 2257 (delta 1624), reused 2257 (delta 1624)
remote: Resolving deltas: 100% (1624/1624), done.
To https://github.com/account/REPO.git
* [new tag] VERSION_0_4_3 -> VERSION_0_4_3
! [rejected] master -> master (fetch first)
! [rejected] VERSION_0 -> VERSION_0 (already exists)
... lots of"rejected" lines...
error: failed to push some refs to 'https://github.com/account/REPO.git'
hint: Updates were rejected because the tag already exists in the remote.

Any ideas? Or does anybody have a process already in place for syncing
CVS to git/GitHub? I've tried stopping before the "push" and doing all
manner of fetches and such, but nothing works. I rarely use git, so I'm
really just reaching out in the dark. The GitHub presence is just to
pick up on a issues and pull requests from folks who are more
comfortable with that interface than e-mail, for which it has worked well.

Thank you,

Kristaps